Review follow-ups:
- Check every PointerMoved / PointerGone of the frame, not only where the
pointer ended: a slow frame merged leaving the row and coming back, so
the slider stayed armed (new test for both events).
- One global armed slider (`wheel_slider_key`) instead of a bool per
slider: unarmed sliders no longer write context data every frame, and
arming another slider disarms the previous one. The wheel remainder is
cleared on arming and disarming, so the second focus check is gone.
- The sideways branch uses `pointer_in_row` too.
- Document that Tab focus arms the arrows only; move the whats-new entry
to 2026-10-21; update the KEY-SLIDER-NUDGE row, header and history; fix
a test comment that described the old remainder carry-over.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
